Within the global wireless telecommunications industry, the current trend in network technology is divided between Global System for Mobile Communications (GSM) and American National Standards Institute (ANSI)-41 based architectures. In many respects, GSM and ANSI-41 based networks are quite similar, with the primary differences between the two technologies simply relating to the protocols used to communicate between the various network entities, and the operating frequencies of the communication handsets themselves. As such, in the interest of clarity, discussions of the present invention will henceforth be limited to GSM type network implementations. However, it should be appreciated that the present invention could be similarly practiced in an ANSI-41, Personal Communication Services (PCS) or similar type network.
A typical GSM network architecture is illustrated in FIG. 1. As shown in FIG. 1, the typical GSM network, generally indicated by the numeral 100, incorporates a number of functional elements or nodes which are appropriately interconnected so as to obtain the desired overall network service. These network nodes include a Home Location Register (HLR) 116, a Visitor Location Register (VLR) 118, an Equipment Identification Register (EIR) 120, an Authentication Center (AuC) 122, a Mobile Switching Center (MSC) 110, a Gateway Mobile Switching Center (GMSC) 112, an Inter-Working Mobile Switching Center (IWMSC) 132, and a Short Message Service Center (SMSC) 130. Briefly, the HLR 116 is a database that is used to store subscriber information for all customers within the home service area of the GSM service provider. Functionally, the HLR 116 is linked through a signaling network to other service areas such that subscriber information may be efficiently shared between geographically diverse networks, a characteristic that facilitates seamless inter-network roaming. Like HLR 116, the VLR 118 is also a database that contains subscriber information. However, the VLR 118 is specifically used to store information related to subscribers who are not in their home service area. More particularly, the VLR 118 is where roaming related data for a customer is stored when the customer activates their handset outside of their designated home service area. The EIR node 120 retains information related to the identification serial numbers of all customer handsets that have been activated within the service area, while the AuC node 122 contains security or encryption key data associated with each of the handsets. SMSC 130 serves primarily as a store-and-forward mechanism for subscribers to send Short Message Service (SMS) messages to other mobile subscribers or computer systems.
The five network elements described above (HLR, VLR, EIR, AuC, SMSC) can be thought of as essentially databases or database processing nodes. Unlike these database nodes, the MSC 110, GMSC 112, and IWMSC 132 are generally identified as network switching elements. Among their many functions, the MSC 110 and GMSC 112 are responsible for determining which cell site will take possession of a call. Such hand off control is facilitated by a communication link between the MSC 110 and an associated Base Station Controller (BSC)/Base Transceiver Station (BTS) pair 124. A Tx/Rx cell site 126 may be associated with each BTS/BSC pair 124. The GMSC 112 has the added distinction of providing a gateway interface to the Public Switched Telephone Network (PSTN) 114; otherwise, MSC 110 and GMSC 112 functionality is very similar. Furthermore, as generally illustrated in FIG. 1, the GMSC 112 is also coupled via signaling links to the four database nodes described above, and as such, all signaling message access to these database nodes is controlled and administered by the GMSC. Although not illustrated in FIG. 1, the MSC may also be coupled directly to the database nodes. IWMSC 132 is typically an MSC 110 or a GMSC 112 that also has the function of inter-working between the SMSC 130 and the rest of the mobile network.
Of particular relevance to the present invention are the signaling aspects of the GSM network described above, especially those aspects associated with the signaling interactions between an HLR or SMSC database node and an MSC or GMSC type node. In order to better understand these signaling interactions, a more detailed explanation of HLR operation is provided below.
Within a GSM wireless communication network, each mobile station handset 128 is assigned a unique identification number known as an International Mobile Subscriber Identity (IMSI) identification number. In the case of European GSM—type network implementations, the IMSI code is typically associated with a particular telephone handset. In such networks, each user can also be assigned one or more Mobile Station Integrated Services Digital Network (MSISDN) numbers. In the wireless telecommunications industry, MSISDN numbers are analogous to the 10 digit telephone numbers in a conventional North American wired network. The fact that multiple MSISDN numbers can be associated with a single IMSI number, indicates that more than one MSISDN number can be assigned and used to reach a single mobile station handset. It should be appreciated that in this disclosure, the term “Mobile Identification Number” (MIN) is used generically to refer to IMSI, MSISDN, Mobile Global Title, ANSI-41 Mobile Identification Numbers (MIN) and Mobile Directory Numbers (MDN), and other identification numbers associated with subscribers or services in a wireless communication network.
In any event, an MSISDN number is dialed whenever a user wants to communicate with a particular mobile station handset. An MSC or GMSC, by analyzing a part of the dialed MSISDN number, determines the particular HLR that is storing routing information associated with the called mobile station. By retrieving and utilizing such routing information, the GSM network is able to locate the called mobile station in response to a call attempt so that a call connection can be established between the calling party and the called mobile station. It should also be appreciated that, depending on the nature of the call or signaling event, an MSC may alternatively analyze and perform the HLR lookup based on the IMSI or MSISDN number associated with the called or calling party.
FIG. 2 illustrates a typical GSM network architecture, generally indicated by the numeral 150, which includes a GMSC 154 that is linked to both an MSC 152 and a single HLR unit 156. GMSC 154 includes a routing table 160, while HLR 156 includes a database table 158. FIG. 3 also illustrates a typical GSM network architecture, generally indicated by the numeral 180, which includes a GMSC 182 linked to several HLR units. More particularly, GMSC 182 is coupled via signaling links to HLR A 186, HLR B 190, and HLR C 194, and necessarily to HLR database tables 188, 192, and 196, respectively. In both FIGS. 2 and 3. GMSCs 154 and 182 may be connected to SS7 network 162
In the examples illustrated in both FIGS. 2 and 3, each of the HLRs is configured to service a pre-defined block of subscriber MSISDN numbers. In general, a specific series or block of MSISDN (or IMSI) numbers are pre-assigned to each HLR in a service provider's network. It should be appreciated that the HLR database and GMSC Routing Table structures shown in FIGS. 2–3 are merely illustrative of the high level information storage concept and are not intended to represent the actual data structures that would typically be implemented in such network nodes. In many cases, service providers are not able to alter these blocks of assigned numbers within a given HLR unit because of routing limitations of the MSC associated with the HLR unit. Consequently, service providers have no opportunity to dynamically re-allocate their MSISDN number base across multiple HLRs, so as to more efficiently utilize existing HLR resources (i.e., load sharing). It should be noted that this limitation is typically the result of routing table restrictions in the MSCs, and generally not database storage restrictions in the HLRs. That is, although HLRs can generally be populated so as to contain subscriber data entries for any IMSI or MSISDN number, MSCs are typically only capable of routing messages based on an IMSI or MSISDN block in which the message's IMSI or MSISDN number falls. These IMSI or MSISDN blocks are comprised of a sequential range of IMSI or MSISDN numbers. Thus, it is the limited routing capability of an MSC or a GMSC that causes the problem, and typically not the HLR nodes.
For instance, in FIG. 2, all traffic relating to calls associated with an MSISDN number between 9199670000 and 9199679999 will be routed to HLR A 156 by the associated GMSC 154. As the service provider begins to acquire more and more customers (i.e., assigning more and more of the MSISDN numbers in the allocated block or series 9199670000 to 9199679999), the traffic or congestion experienced at the HLR A 156 node will increase accordingly.
Now consider that a service provider owning the network elements illustrated in FIG. 2 has acquired so many new customers that it is decided to invest in an additional pair of HLRs. This scenario is generally illustrated in FIG. 3, where the two additional HLRs are identified as HLR B 190 and HLR C 194. At the time of implementation HLR B 190 is populated with MSISDN number block 919968000–9199689999, and HLR C 194 is populated with MSISDN number block 9199690000–9199699999. These two HLRs are linked to the adjacent GMSC 182 and activated so as to service any calls corresponding to their pre-programmed MSISDN blocks.
The major shortcoming of such multiple HLR configurations can now be more fully appreciated. As generally indicated in FIG. 3, despite the addition of the new HLR resource capacity represented by units B and C, all call traffic associated with MSISDN numbers 9199670000–9199679999 must still be handled by a single HLR, HLR A 188. Even if the service provider has no customers within the MSISDN 9199680000–9199699999 number range, it is not possible for the service provider to dynamically re-allocate or re-distribute the “fully assigned” 9199670000–9199679999 MSISDN number block among the unused HLR B 192 and HLR C 196 units. Thus, it is quite possible that the service provider will operate in a situation where traffic to HLR A 188 is highly congested, while the HLR B 192 and HLR C 196 resources are completely unused. This can lead to less than efficient usage of installed resources, as it would be more efficient to load balance or share traffic more equally among the three HLR units.
It should be appreciated that, in addition to the load sharing concerns, there are similar issues and similar needs that arise when considering the porting of subscribers from one service provider to another, otherwise known as local number portability (LNP). Once again, the central problem is the ability to freely distribute subscriber information among multiple HLR nodes. A detailed discussion of the specific problems associated with LNP is not provided in this disclosure, as the high-level issues and concerns are the same as those for the load sharing scenario described herein.
U.S. Pat. No. 5,878,347 to Joensuu, et al., (hereinafter, “the '347 Patent”) the disclosure of which is hereby incorporated by reference in its entirety, discloses one approach to solving some of the problems identified and discussed above. The solution described in the '347 Patent involves the implementation of a new network element, referred to as a virtual HLR (vHLR). FIG. 4 of the present application and the following description illustrates the function of the vHLR in the '347 patent. Referring to communication network 210 illustrated in FIG. 4, a vHLR node 214 is placed in the communication network pathway between a GMSC 212 and a plurality of HLR nodes, HLR A 218, HLR B 222, and HLR C 226. HLRs 218, 222, and 226 contain subscriber databases 220, 224, 228, respectively. The GMSC 212 sends signaling messages to the vHLR node 214 requesting subscriber information where the particular subscriber is associated with an IMSI or MSISDN type mobile station identification number. The vHLR 214 does not contain subscriber information; rather, the vHLR 214 contains a routing table 216 that correlates IMSI or MSISDN numbers with a particular HLR. More particularly, the routing table 216 contains information relating IMSI or MSISDN numbers to a corresponding network address associated with the HLR serving that IMSI or MSISDN subscriber.
The message routing technique disclosed by the '347Patent is a key element of the invention described therein. As generally illustrated in FIG. 4, a call originating from SS7 network 162 results in MSISDN=919969000 being communicated to GMSC 212. GMSC 212 originates a message 234 and sends the message to vHLR 214. When the vHLR node 214 receives a message 234 from the associated GMSC 212, the message is addressed to and is delivered directly to the vHLR node 214. The vHLR node 214 performs a table lookup, as described above, and re-routes the message to the appropriate HLR node, in this case HLR C 228. This re-routing function is accomplished by altering the destination point code (DPC) of the message 236 routing label, such that the original DPC (PC=vHLR) is replaced by a new DPC (PC=HLR C). It is significant, and should be noted that the vHLR node 214 does not alter the origination point code (OPC) of the message routing label. That is, the OPC of the incoming message 234 is the same as the OPC of the outgoing message 236, which is the point code of the GMSC 212. Thus, the message arrives at HLR C 228 with an OPC equal to the point code of GMSC node 212. HLR C 228 then responds with a message 238 that is addressed to the GMSC 212. The HLR C response message 238 is not routed back through the vHLR node 214.
While such a routing technique may save one or more routing “hops”, from a network management perspective, this routing technique presents at least one significant problem. That is, in the event that an HLR should become unable to provide service, SS7 signaling convention requires that the HLR send a message to any signaling point (SP) that is attempting to communicate with it, alerting the SP to the impaired or out-of-service status of the HLR. Given the message flow described above, it will be appreciated that in such an out-of-service scenario, HLR C 226 would send a network management message to the originator of the incoming HLR C message 236. The originator of the incoming HLR C message 236 is identified by the OPC field of the message 236 routing label. As described above, the vHLR 214 node does not alter the OPC field of the routing label, but instead leaves the OPC set to the address of the GMSC 212. Thus, network management messages sent by HLR C 226 will be addressed to the GMSC 212. The problem with such a message routing scheme is that the GMSC 212 has no “knowledge” of having sent a message to HLR C 226. Once again, it will be appreciated that the DPC of the message 234 originally sent by the GMSC 212 was the network address of the vHLR 214. That is, the GMSC 212 has knowledge of a message sent to the vHLR 214, but no knowledge of a particular message destined for HLR C 226. Implementation of such an SS7 message routing scheme would therefore present a large problem for SS7 network operators that have purchased and deployed a large number of network elements that operate in compliance with industry standard SS7 communication protocols and network management procedures.
Therefore, what is needed is a novel system and method of redirecting signaling messages among multiple HLR, EIR, AuC and other similar signaling database type nodes, where message routing occurs in such a way as to preserve compliance with existing industry standard network management signaling protocols.